The field of the disclosure relates generally to noise attenuation, and, more particularly, to a noise attenuating lipskin assembly and methods of assembling the same.
At least some known engines, such as some known jet engines and turbofan jet engines, are surrounded by a generally barrel-shaped nacelle. At least some known nacelles include a lipskin assembly at an inlet of the nacelle that at least partially defines a plenum configured to receive heated air for transpiring through the lipskin assembly to reduce ice formation on the nacelle. As such, at least some known lipskin assemblies provide structural strength, noise attenuation, and ice prevention measures for the nacelle. In one example, such as U.S. Pat. No. 6,688,558, the entirety of which is hereby incorporated herein by reference, at least one known lipskin assembly includes a perforated backsheet, a honeycomb core coupled to a forward side of the backsheet, and a perforated lipskin coupled to a forward side of the core. Heated air flows through the perforated backsheet, into the core, and transpires through the perforated lipskin to prevent ice from forming on the nacelle. Furthermore, sound waves generated inside the engine propagate forward and enter the cells of the honeycomb core through the lipskin and reflect from the backsheet at a phase different from the entering sound waves to facilitate damping the incoming sound waves and attenuating the overall noise level.
Moreover, at least some known lipskin assemblies include a nearly linear lipskin, that is, a material that responds substantially the same to acoustic waves regardless of the sound pressure (i.e., amplitude) of the waves, to facilitate noise attenuation. For example, in at least some known lipskin assemblies, the lipskin is uniformly covered with perforations that each have a diameter on the order of a few hundredths of an inch. Typically, the perforations are arranged such that the lipskin has a porosity of from 3 to 10 percent open area. The linearity of the lipskin increases with the density of such perforations. However, the linearity, and thus the acoustic performance, of at least some known lipskins is limited because a cost and a time required to form more of the small perforations with a necessary precision is prohibitive.